Significantly enhanced energy storage performance in Sm-doped 0.88NaNbO3-0.12Sr0·7Bi0·2TiO3 lead-free ceramics

Lead-free antiferroelectric (AFE) ceramic materials have attached increasing attention in application of high-power capacitors for the past few years, due to their high energy storage density and environmental protection. However, the related applications are seriously restricted because of the limited number of environment friendly AFE candidate materials, high cost and low energy storage efficiency. In this work, the A-site ion Sm³⁺ doped 0.88NaNbO₃-0.12Sr_0·7Bi_0·2TiO₃ lead-free AFE P phase ceramics (0.88Na_1-3xSm_xNbO₃-0.12Sr_0·7Bi_0·2TiO₃, abbreviated as NN-SBT-100xSm) were prepared and characterized. With the increase of Sm doping amount, a relaxor-like behavior was found in the dielectric-temperature curves of NN-SBT-100xSm, indicating the AFE orthorhombic P phase is gradually replaced by an AFE orthorhombic R phase. As a result, double-like and slim P-E curve with near-zero residual polarization and suppressed hysteresis loss was obtained at x > 0.01. More encouragingly, a good discharge energy storage density (W_rec = 3.58 J/cm³) and a high efficiency (η = 82%) at a low electric field (E = 200 kV/cm) has been recorded simultaneously for NN-SBT-2Sm relaxor AFE ceramic, which are better than the other lead-free energy storage ceramics under the same E. In addition, the energy storage properties of NN-SBT-2Sm ceramics exhibit outstanding temperature and frequency stability. These results indicate that NN-SBT-2Sm relaxor AFE ceramic has a great practical value in pulse power capacitors.     

Dielectric and Raman Spectroscopic Studies of Na0.5Bi0.5TiO3–BaSnO3 Ferroelectric System

A series of lead‐free perovskite solid solutions of (1 ? x) Na_0.5Bi_0.5TiO₃(NBT)—x BaSnO₃(BSN), for 0.0 ≤ x ≤ 0.15 have been synthesized using a high‐temperature solid‐state reaction route. The phase transition behaviors are studied using dielectric and Raman spectroscopic techniques. The ferroelectric to relaxor phase transition temperature (T_FR) and the temperature corresponding to maximum dielectric permittivity (T_m) are estimated from the temperature‐dependent dielectric data. Dielectric studies show diffuse phase transition around ~335°C in pure NBT and this transition temperature decreases with increase in x. The disappearance of x‐dependence of A₁ mode frequency at ~134 cm^?1 for x ≥ 0.1 is consistent with rhombohedral‐orthorhombic transition. In situ temperature dependence Raman spectroscopic studies show disappearance and discontinuous changes in the phonon mode frequencies across rhombohedral (x < 0.1)/orthorhombic (x ≥ 0.1) to tetragonal transition.     

Large direct and inverse electrocaloric effects in lead-free Dy doped 0.975KNN-0.025NBT ceramics

Undoped and Dy³⁺ doped 0.975 K_1/2Na_1/2NbO₃-0.025Na_1/2Bi_1/2TiO₃ (0.975KNN-0.025NBT) ceramics were synthesized using the solid-state synthesis method. X-ray diffraction analysis revealed pure perovskite structure without any secondary phases. The dielectric investigations of both ceramics revealed low dielectric losses in the dysprosium doped ceramic, particularly for temperatures higher than 100 °C. The dielectric loss anomaly around room temperature corroborates the polymorphic phase boundary (PPB) between orthorhombic and tetragonal phases detected by XRD investigations. The electrocaloric effect (ECE) was investigated using the indirect method based on the Maxwell equation and thermal P–E hysteresis loops. The maximum ECE value was found equal to 0.63 K at 83 °C for KNNBT0.025. However, in Dy doped KNNBT0.025 ceramics, both direct and inverse ECE responses were found with values of 1.01 K at 118 °C and −1.79 K at 80 °C, respectively. Besides, yellow light emission was detected under an excitation wavelength of 350 nm. The simultaneous existence of high ECEs, good dielectric performance, and photoluminescence properties makes KNNBT-Dy a promising candidate for solid-state refrigeration and optoelectronic devices.     

Dielectric temperature stability of Nb-modified Bi0.5(Na0.78K0.22)0.5TiO3 lead-free ceramics

In this study, the phase structure, microstructure and dielectric properties of Bi_0.5(Na_0.78K_0.22)_0.5(Ti_1-xNb_x)O₃ lead-free ceramics prepared by traditional solid phase sintering method were studied. The second phase pyrochlore bismuth titanate (Bi₂Ti₂O₇) was produced in the system after introduction of Nb⁵⁺. The dielectric constant of the sample (x = 0.03) sintered at 1130 °C at room temperature reached a maximum of 1841, and the dielectric loss was 0.045 minimum. It had been found that the K⁺ and Nb⁵⁺ co-doped Bi_0.5Na_0.5TiO₃ (BNT) lead-free ceramics exhibited outstanding dielectric-temperature stability within 100–400 °C with T_cc ≤±15%. Result of this research provides a valuable reference for application of BNT based capacitors in high temperature field.     

New Antiferroelectric Solid Solution of Pb(Mg1/2W1/2)O3–Pb(Zn1/2W1/2)O3 as Dielectric Ceramics

A new solid solution of (1?x)Pb(Mg_1/2W_1/2)O₃–xPb(Zn_1/2W_1/2)O₃ has been prepared in the form of ceramics by solid‐state reaction with composition x up to 30%. It is found that with the substitution of Zn²⁺ for Mg²⁺ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T_C of PMW increases from 40°C (x = 0) to 67°C (x = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X‐ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group (Pmcn) with a decrease in lattice parameter a, but an increase in b and c as the Zn²⁺ concentration increases. The low dielectric constant (~ 10²), low dielectric loss (tanδ ≈ 10^?3), linear‐field‐induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.     

High performance lead-free piezoelectric 0.96(K0.48Na0.52)NbO3-0.03[Bi0.5(Na0.7K0.2Li0.1)0.5]ZrO3-0.01(Bi0.5Na0.5)TiO3 single crystals grown by solid state crystal growth and their phase relations

0.96(K_0.48Na_0.52)NbO₃-0.03[Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5]ZrO₃-0.01(Bi_0.5Na_0.5)TiO₃ single crystals were grown for the first time by the solid state crystal growth method, using [001] or [110]-oriented KTaO₃ seed crystals. The grown single crystal shows a dielectric constant of 2720 and polarization-electric field loops of a lossy normal ferroelectric, with P_r = 45 μC/cm² and E_c = 14.9 kV/cm, while the polycrystalline samples with a dielectric constant of 828 were too leaky for P-E measurement due to humidity effects. The single crystal has orthorhombic symmetry at room temperature. Dielectric permittivity peaks at 26 °C and 311 °C, respectively, are attributed to rhombohedral-orthorhombic and tetragonal–cubic phase transitions. Additionally, Raman scattering shows the presence of an orthorhombic-tetragonal phase transition at ∼150 °C, which is not indicated in the permittivity curves but by the loss tangent anomalies. A transition around 700 °C in the high temperature dc conductivity is suggested to be a ferroelastic-paraelastic transition.     

Phase transition behavior of Pb(Hf,Sn, Ti,Nb)O3 ceramics at morphotropic phase boundary

The phase transition and dielectric properties of Pb_0.988(Hf_0.945Sn_xTi_0.03-xNb_0.025)O₃ ceramics (0 ≤ x ≤ 0.03, correspondingly abbreviated as H1, H2, H3, and H4) at the morphotropic phase boundary were systematically investigated. X-ray diffraction results and P-E hysteresis loops show that the dominate orthorhombic antiferroelectric phase and a small amount of the tetragonal FE phase coexist in Pb_0.988(Hf_0.945Sn_xTi_0.03-xNb_0.025)O₃ ceramics. As the Sn content increases, the antiferroelectricity is significantly enhanced, accompanied with an increased Curie temperature and sharply reduced peak dielectric constant. H1 and H2 experience an irreversible field-induced AFE-FE phase transition at the ambient temperature, and the transition from a metastable FE phase to the original AFE phase is observed in H2 when heated to 60°C. H3 and H4 experience an invertible AFE-FE phase transition, along with an enhanced forward phase switching field E_F. Moreover a decreased backward phase switching field E_A for H4 is detected as the electric field increases due to the AFE/FE coexistence. These results reveal the unique phase transition characteristics of AFE materials near the phase boundary, which is helpful for better understanding of AFE/FE materials.     

Synthesis,structure, and dielectric properties of a new binary antiferroelectric solid solution: (1−x)Pb(Mg1/2W1/2)O3–xPbHfO3

Dielectric ceramics are one of the most important electrical insulators because of their excellent electrical stability and nonconducting properties. In this work, new complex perovskite solid solutions, (1−x)Pb(Mg_1/2W_1/2)O₃–xPbHfO₃ [(1−x) PMW–xPHf] (0.00 ≤ x ≤ 0.04), were successfully synthesized in the form of ceramics by the solid-state reaction method and sintering process. The X-ray diffraction results indicate that a single perovskite phase with antiferroelectric (AFE) orthorhombic Pmcn symmetry is formed for x < 0.04 which corresponds to the PMW-type solid solution (SS-PMW). For the composition x = 0.04, however, a small amount (about 1%) of ferroelectric orthorhombic C2mm phase that arises from the PHf-type solid solution (SS-PHf) was found to coexist with the Pmcn phase (99%). The dielectric measurements show that the AFE-paraelectric phase transition temperature T_C of the (1−x)PMW–xPHf ceramics increases from 38.2°C (x = 0) to 40.1°C (x = 0.03) with the increasing PHf content, indicating a slightly enhanced AFE ordering degree. The studied materials show a relatively low dielectric constant (~10²), a low dielectric loss (~10⁻²), a high breakdown field strength (~140 kV/cm), and a linear electric field dependence of polarization at room temperature, which make them a new candidate for potential applications as ceramic insulators.     

Giant strains of 0.70% achieved via a field-induced multiple phase transition in BNT-based relaxor antiferroelectric ceramics

Bismuth sodium titanate (BNT)-based lead-free ceramics have attracted a great deal of attention due to their large electrostrains. In this work, a remarkably symmetric strain of 0.7% together with excellent temperature (0.5–0.7% from 25 to 100 °C)/frequency (ΔS<4% from 1 to 20 Hz) stability was observed in the 0.91(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.03NaNbO₃ (BNT-6BT-3NN) AFE P4bm ceramic through constructing R3c/P4mm/P4bm triple-phase coexistence phase boundary. Compared with other two compositions near double-phase coexistence ferroelectric (FE)-antiferroelectric (AFE) phase boundaries, the BNT-6BT-3NN ceramic exhibits a unique field-induced multiple phase transition from the initial AFE P4bm phase to the metastable FE P4mm phase and finally into the FE R3c phase. In-situ structural analysis evidenced a significantly enhanced lattice strain but a comparable strain value from domain switching in BNT-6BT-3NN compared with other compositions. The present study provides a novel strategy for designing high-performance large-strain ceramics in BNT-based relaxor AFE systems.     

High-temperature dielectric and relaxation behavior of Yb-doped Bi0.5Na0.5TiO3 ceramics

Microstructure, phase transition and dielectric properties of Yb-doped Bi_0.5Na_0.5TiO₃ (BNT) ceramics were investigated. It is found that ytterbium promotes the grain growth and densification of the ceramics while Ti-rich impurity appears due to the compensation of Ti-vacancy. The dielectric operational temperature range of the ceramics with a±15% tolerance was greatly broaden until 500 °C by ytterbium doping. Meanwhile, the diffuseness of the diffuse phase transition increases with the increase of doping Yb. BNT ceramics with 3 mol% Yb doping shows a near-plateau dielectric behavior in a broad temperature range from 147 to 528 °C and a low dielectric loss (<0.025) from 154 to 356 °C, indicating that it is a promising material for applications in high-temperature capacitor.     

Antiferroelectric‐ferroelectric phase transition in lead‐free AgNbO3 ceramics for energy storage applications

The high‐energy storage density reported in lead‐free AgNbO₃ ceramics makes it a fascinating material for energy storage applications. The phase transition process of AgNbO₃ ceramics plays an important role in its properties and dominates the temperature and electric field dependent behavior. In this work, the phase transition behavior of AgNbO₃ ceramics was investigated by polarization hysteresis and dielectric tunability measurements. It is revealed that the ferrielectric (FIE) phase at room temperature possesses both ferroelectric (FE)‐like and antiferroelectric (AFE)‐like dielectric responses prior to the critical AFE‐FE transition point. A recoverable energy storage density of 2 J/cm³ was achieved at 150 kV/cm due to the AFE‐FE transition. Based on a modified Laudau phenomenological theory, the stabilities among the AFE, FE and FIE phases are discussed, laying a foundation for further optimization of the dielectric properties of AgNbO₃.     

Investigation of the Structure and Electrical Properties of (KxNa0.96−xLi0.04)(Nb0.96−yTaySb0.04)O3 Piezoelectric Ceramics Modified with Manganese

The effect of high doping levels of manganese (Mn) on the structure and electrical properties of (K_xNa_1?x)NbO₃ (KNN) ceramics containing Li, Ta, and Sb has been investigated. The samples were measured using synchrotron X‐ray diffraction whereas Rietveld refinement with Fullprof was used to determine the structural information as a function of temperature. Temperature‐dependent dielectric measurement was used to compare the phase transition temperatures. The results show that Mn decreases the temperature range of phase coexistence between the orthorhombic and tetragonal phase from ~180°C to ~120°C. The Curie temperature remained unchanged with Mn addition while the dielectric constant and dielectric loss increased with Mn addition. High amounts of Mn led to a reduction in both piezoelectric and ferroelectric properties. The remnant polarization, remnant strain, and piezoelectric coefficient values decreased from 24 μC/cm², 0.000824, 338 ± 37 pm/V to 13 μC/cm², 0,00014 and 208 ± 27 pm/V, respectively for the undoped and 5 mol% Mn‐doped sample.     

Excellent energy-storage property and thermal stability of PLZT-based antiferroelectric ceramics

(Pb, La)(Zr, Ti)O₃ antiferroelectric (AFE) materials are promising materials due to their energy-storage density higher than 10 J cm⁻³, but their low energy-storage efficiency and poor temperature stability limit their application. In this paper, the (1 − x)(Pb_0.9175La_0.055)(Zr_0.975Ti_0.025)O₃–xPb(Yb_1/2Nb_1/2)O₃ (PLZTYN100x) AFE ceramics were prepared via two-step sintering method and investigated thoroughly. With the doping of Yb³⁺ and Nb⁵⁺, the phase structure transforms from the orthorhombic phase (AFE_O) to the coexistence of the orthorhombic-and-tetragonal phases. This structure reduces the free energy difference between the AFE and ferroelectric phases and reduces the fluctuation of energy with temperature, improving the energy storage efficiency and temperature stability. When the x = 0.05 (PLZTYN5), the AFE ceramic exhibits excellent temperature stability and ultrahigh energy storage performance, whose recoverable energy density (W_rec) is 6.8–8.2 J cm⁻³ at 30 kV mm⁻¹ in the temperature range from −55 to 75°C, and efficiency (ƞ) is 78%–86.7%. In addition, the change of W_rec is less than 15%, exceeding the performance of most AFE ceramics. The results demonstrate that the PLZTYN5 ceramic has great potential in pulse power capacitors.     

Temperature‐stable dielectric and energy storage properties of La(Ti0.5Mg0.5)O3‐doped (Bi0.5Na0.5)TiO3‐(Sr0.7Bi0.2)TiO3 lead‐free ceramics

A new type of (0.7?x)Bi_0.5Na_0.5TiO₃‐0.3Sr_0.7Bi_0.2TiO₃‐xLaTi_0.5Mg_0.5O₃ (LTM1000x, x = 0.0, 0.005, 0.01, 0.03, 0.05 wt%) lead‐free energy storage ceramic material was prepared by a combining ternary perovskite compounds, and the phase transition, dielectric, and energy storage characteristics were analyzed. It was found that the ceramic materials can achieve a stable dielectric property with a large dielectric constant in a wide temperature range with proper doping. The dielectric constant was stable at 2170 ± 15% in the temperature range of 35‐363°C at LTM05. In addition, the storage energy density was greatly improved to 1.32 J/cm³ with a high‐energy storage efficiency of 75% at the composition. More importantly, the energy storage density exhibited good temperature stability in the measurement range, which was maintained within 5% in the temperature range of 30‐110°C. Particularly, LTM05 show excellent fatigue resistance within 10⁶ fatigue cycles. The results show that the ceramic material is a promising material for temperature‐stable energy storage.     

Phase transition and negative thermal expansion properties in isovalently substituted In2−xScx(MoO4)3 ceramics

Sc-substituted In_2−xSc_x(MoO₄)₃ (0 ≤ x ≤ 2) ceramics were successfully synthesized by the solid state reaction method with the goal of tuning the phase transition temperature. Effects of Sc³⁺ substitution on the phase composition, microstructure, phase transition temperature and thermal expansion behavior of the In_2−xSc_x(MoO₄)₃ (0 ≤ x ≤ 2) ceramics were investigated using XRD, FESEM, EDX, XPS and TMA, respectively. The results indicate that all samples are single phase. The relative densities of the In_2−xSc_x(MoO₄)₃ ceramics increased gradually with increasing Sc³⁺ content. Investigations on thermal expansion properties of the In_2−xSc_x(MoO₄)₃ ceramics reveal that the temperature-induced phase transition from monoclinic to orthorhombic symmetry is strongly correlated to the Sc³⁺ content. The obtained In₂(MoO₄)₃ ceramics undergoes a structural phase transition from monoclinic to orthorhombic around 355.3 °C. The phase transition temperature can be significantly shifted from 355.3 °C (x = 0) to 31.9 °C (x = 1.5) by partially replacing In³⁺ cations with less electronegative Sc³⁺ cations. All In_2−xSc_x(MoO₄)₃ (0 ≤ x ≤ 2) ceramics exhibit strong negative thermal expansion above the phase transition temperature. In_0.5Sc_1.5(MoO₄)₃ exhibits linear NTE over the 100–700 °C temperature range with a linear coefficient of thermal expansion of −3.99 × 10⁻⁶ °C ⁻¹.     

Dielectric Properties of Sol–Gel‐Derived Bi12SiO20 Thin Films

In this paper the dielectric properties of crack‐free, Bi₁₂SiO₂₀ thin films were investigated. The films were prepared on Pt/TiO₂/SiO₂/Si and corundum substrates using the sol–gel method. The formation of a pure Bi₁₂SiO₂₀ phase was observed at a temperature of 700°C. The Bi₁₂SiO₂₀ thin films, heat treated at 700°C for 1 h, had a dense microstructure with an average roughness (R_a) of 50 nm. The dielectric properties of the film were characterized by using both low‐ and microwave‐frequency measurement techniques. The low‐frequency measurements were conducted with a parallel capacitor configuration. The dielectric constant and dielectric losses were 44 and 7.5 × 10^?3, respectively. The thin‐film dielectric properties at the microwave frequency were measured using the split‐post, dielectric resonator method (15 GHz) and the planar capacitor configuration (1–5 GHz). The dielectric constant and the dielectric losses measured at 15 GHz were 40 and 17 × 10^?3, respectively, while the dielectric constant and the dielectric losses measured with the planar capacitor configuration were 39 and 65 × 10^?3, respectively.     

Effect of Nd substitution on the microstructure and electrical properties of Bi7Ti4NbO21 piezoceramics

Neodymium (Nd) doped intergrowth bismuth layer-structured ferroelectric compounds Bi_7?xNd_xTi₄NbO₂₁ (x = 0, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0) were synthesized through a solid-state method. The influence of the Nd³⁺ substitution of Bi³⁺ on the lattice, microstructure and electrical properties of these compounds were investigated. The X-ray diffraction and Raman scattering analyses demonstrate that a phase transition from orthorhombic to pseudo-tetragonal occurs in these compounds, relying on substitution proportions and sites of Nd³⁺ for Bi³⁺. With the increasing Nd³⁺ dopants, the growth of plate-like grains along the a–b plane and a secondary intergranular metallic Bi phase were retarded which resulted in the increases of sintering temperature, density and electrical resistance of the doped ceramics. The resultant ceramic with x = 1.25 possesses a piezoelectric coefficient d₃₃ up to 16.3 pC/N with a Curie temperature T_C above 750 °C were obtained for the compound.     

Internal friction investigation of phase transformation in nearly stoichiometric LaMnO3+δ

Rhombohedral LaMnO_3+δ powders, prepared by two different soft chemistry routes (co-precipitation and hydrothermal synthesis), are sintered at 1400 °C for 2 h in air. Measurements of internal friction Q⁻¹(T) and shear modulus G(T), at low frequencies from −180 to 700 °C under vacuum, evidence three structural transitions of nearly stoichiometric orthorhombic LaMnO_3+δ. The first one, at 250 or 290 °C, depending on the processing followed, is associated to either a Jahn–Teller structural transition or a phase transformation from orthorhombic to pseudo-cubic. The second one at 610 or 630 °C is related to a phase transformation from pseudo-cubic or orthorhombic to rhombohedral. Below the Neel temperature, around −170 °C, a relaxation peak could be associated, for samples prepared according to both processing routes, to the motion of Weiss domains.     

Phase structure and electrical properties of lead free Na0·5Bi0·5TiO3–CaTiO3 ceramics

Abstract

Abstract

(1?x)Na_0·5Bi_0·5TiO_3?xCaTiO₃ ceramics with x?=?0–0·2 were prepared by solid state sintering method. Structural and morphology studies carried out by X-ray diffraction and scanning electron microscopy indicate the change in crystal structure from rhombohedral to orthorhombic symmetry (R3C to Pnma). The morphotropic phase boundary of this system was found to lie around x?=?0·08–0·14, where the orthorhombic and rhombohedral symmetries coexist. The orthorhombic phase is stabilised for x>0·14, indicating that the rhombohedral phase of Na_0·5Bi_0·5TiO₃ is susceptible to orthorhombic distortion brought about by Ca substitution. Calcium substitution in Na_0·5Bi_0·5TiO₃ caused an obvious decrease in peak temperature and a decrease in relative permittivity. The compositional variation of the fundamental dielectric behaviour is discussed in relation to the crystal chemistry of the system. The highest piezoelectric constant d₃₃ of 85 pC N^?1 is achieved for x?=?0·1, with the coercive field of 18 kV cm^?1 and the dielectric maximum temperature of 148°C.     

Luminescence and electrical properties of Eu-modified Bi0.5Na0.5TiO3 multifunctional ceramics

The Eu³⁺-modified Bi_0.5Na_0.5TiO₃ (BNT) ceramics have been fabricated by the solid-state reaction method. The impact of Eu³⁺ doping on the structure, photoluminescence, and electrical properties has been studied by XRD, SEM, PL spectra, and LCR meter. X-ray diffraction analysis reveals that the crystal structure of the samples is well matched with the trigonal perovskite, and the optimal temperature of presintering is 880°C. The Eu³⁺-doped BNT ceramics show excellent red fluorescence at 614 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ under 466 nm excitation and relatively long fluorescence lifetime. The BNT-0.02Eu ceramic density is up to 5.68 g/cm³ and the relative density is up to 94.6% with sintering temperature 1075°C. The piezoelectric constant (d₃₃) of samples has been significantly improved up to 110 pC/N by Eu³⁺ doping. The BNT-0.03Eu ceramic presintered at 880°C and sintered at 1050°C has good dielectric properties and excellent luminescence properties. Eu³⁺-doped BNT ceramics make it potential applications for novel integrated electro-optical and multifunctional devices.